Die, method of manufacturing stepped metal pipe or tube, and stepped metal pipe or tube

Abstract

The through hole of a die has an inside surface including a bell portion, an approach portion, and a bearing portion from the entrance side formed in a continuous manner. The diameter of the approach portion is D 1 on the entrance side of the approach portion and D 2 on the exit side of the approach portion and gradually decreases from the entrance side to the exit side. The diameter satisfies Equation (1): 0.7≦D 2 /D 1 <0.97. The die half angle of an inside surface where the diameter D 3 is D 2 /0.97 is not less than the die half angle R 2 of an inside surface nearer to the exit side of the approach portion than the inside surface where the diameter is D 3 , and the axial distance LR from the inside surface where the diameter is D 3 to the inside surface where the diameter is D 2 satisfies Equation (2): 20≦LR/((D 3 −D 2 )/2)≦115. The diameter of the through hole at the bearing portion is fixed at D 2 , and the length is LB and satisfies Equation (3): 0.3≦LB/D 2 ≦10.

1 - 3 . (canceled)  
   
   
       4 . A stepped metal pipe or tube including a first hollow cylindrical portion, a taper portion, and a second hollow cylindrical portion formed in a continuous manner, wherein the outside diameter of said first hollow cylindrical portion is DA, 
 the outside diameter of said second hollow cylindrical portion is DB that is smaller than said DA,    the outside diameter of said taper portion gradually decreases from said first hollow cylindrical portion to the second hollow cylindrical portion as the value of the outside diameter decreases from DA to DB, and the axial distance LE from the surface where the outside diameter DC is DB/0.97 to the surface where the outside diameter is DB satisfies Equation (4):      20 ≦LE /(( DC−DB )/2)≦115  (4)